Endoluminal prostheses are used for reinforcing or repairing blood vessels and other lumens within the body. For example, arteries narrowed or occluded by stenosis, thrombosis, or aneurysm may be reinforced, with or without additional surgical procedures such as angioplasty, by placing a prosthesis in the diseased portion of the artery. Such prostheses may be deployed within a body lumen by minimally invasive endoluminal insertion techniques. These include “surgical cut-down” procedures in which a small incision is made in the vasculature, for example in the femoral artery in the leg or in an artery in the shoulder of a patient, and a catheter is inserted at that location into the vessel. The catheter is maneuvered to the desired point of deployment, and the prosthesis is advanced through the catheter to that point. During this insertion process, the prosthesis is in a reduced diameter configuration, smaller than its intended diameter for use in repairing the vessel. The prosthesis is then expelled from the catheter into the vessel and expanded, with or without additional manipulation, into its intended use diameter within the vessel. The catheter is then removed from the body. Alternatively, percutaneous access may be used, wherein a needle puncture rather than a surgical incision is used to gain access to the vasculature. Percutaneous techniques are used for inserting relatively small prostheses; surgical cut-down techniques are used for relatively large ones.
A typical known insertion catheter consists of an outer sheath having a pusher slidably disposed within it. See, for example, U.S. Pat. No. 5,405,377 to Cragg. Once the catheter is inserted in the vessel and the prosthesis is advanced to the desired location within the vessel, the pusher is held in place while the outer sheath is retracted. This effectively discharges the prosthesis from the catheter.
For some prostheses, this simple pusher-in-sheath catheter arrangement is insufficient. An example of such a prosthesis is one having multiple diameters along its axis, such as the bifurcated prosthesis described in U.S. Pat. No. 5,609,627 to Goicoechea et al. The bifurcated prosthesis described in that patent has a stent portion having a first diameter adapted to be disposed in an aorta, and a branch portion having a second diameter, smaller than the first diameter, that extends into one of the iliac arteries. To insert such a multi-diameter stent, a multi-sheath delivery catheter is required.
It is also occasionally necessary to use a multi-sheath catheter to deliver a conventional straight prosthesis. With some prostheses, significant frictional forces exist between the prosthesis and the outer sheath of the catheter in which it is contained for transport to the delivery location and deployment. This may be the case with relatively long prostheses because friction increases as the outer surface area of the prosthesis increases.
A known multi-sheath delivery catheter 10 is illustrated in FIG. 1. Multi-sheath catheter 10, similar to that disclosed in Goicoechea '627, comprises outer sheath 11, middle sheath 12, and pusher 13. Outer sheath 11 and middle sheath 12 are designed to be of an optimum diameter for containing the aortic portion and one bifurcated leg portion, respectively, of the bifurcated stent described above.
Outer sheath 11, middle sheath 12, and pusher 13 are concentrically slidably disposed relative to one another and are diametrically sized such that the prosthesis does not buckle against pusher 13 during deployment. In order to deploy a prosthesis contained within outer sheath 11 and middle sheath 12, catheter 10 is first percutaneously inserted to the desired delivery location within a body lumen according to methods known in the art. Outer sheath 11 is then retracted while middle sheath 12 and pusher 13 are held stationary. This action releases the first portion of the prosthesis that had been contained by outer sheath 11 because stationary middle sheath 12 and pusher 13 effectively prevent the first and second portions, respectively, of the prosthesis from moving as outer sheath 11 is retracted. Outer sheath 11 and middle sheath 12 are then retracted together while pusher 13 is held stationary to complete deployment of the prosthesis.
During this deployment, it is important that the tubes do not rotate with respect to one another. Rotation of any one of the tubes independently along its axis will not rotate the others. Such rotation could cause twisting or misalignment of the prosthesis being delivered. This also makes it difficult to gauge the twist or orientation of the prosthesis within the catheter, which is critical for aligning bifurcated prostheses with the anatomy. In addition, if the concentric tubes described above are not withdrawn in the proper order, the system will not properly deploy the prosthesis. Care must thus be exercised by a physician using a multi-sheath catheter to implant a prosthesis to retract the tubes in proper order.
An improved multi sheath delivery catheter for deployment of endoluminal prostheses is desired.